1. Field of the Invention
This invention relates to a power source filter circuit, and more particularly relates to a power source filter circuit that is capable of eliminating noise component supplied from a power source and driving noise component generated from an induction load simultaneously.
2. Description of the Related Art
A xcfx80-filter circuit and T-type filter circuit have been known as the typical conventional power source filter circuit connected between a direct current power source and a load circuit. In this case, a xcfx80-type filter circuit comprises an inductor connected in series between an input terminal and an output terminal, a first capacitor connected between the input terminal and a reference potential point, and a second capacitor connected between the output terminal and the reference potential point. On the other hand, a T-type filter circuit comprises a first inductor and a second inductor connected in series between an input terminal and an output terminal, and a capacitor connected between the contact point formed between the first inductor and the second inductor and a reference potential point. An inductance value of the inductor and the capacitance value of the first capacitor and second capacitor are selected suitably in the case of the xcfx80-type filter circuit, and on the other hand the inductance value of the first inductor and the second inductor and a capacitance value of the capacitor are selected suitably in the case of the T-type filter circuit to filter and eliminate effectively various noise components included in a direct current supplied from a power source and supply a direct current rid of various noise components to a load.
Furthermore, in the case where various noise components are included in a direct current supplied from a direct current power source, it has been known that a double xcfx80-type filter circuit that is formed of two cascade-connected xcfx80-type filter circuits is used or a double T-type filter circuit that is formed of two cascade-connected T-type filter circuits is used as the power source filter circuit.
The xcfx80-type filter circuit and the T-type filter circuit that have been used for the known power source filter circuit are capable of filtering and eliminating various noise components included in a direct current supplied from a direct current power source to thereby prevent such various noise components from being supplied to a load. However, in the case where an inductive load such as a motor is connected as the load and the inductive load generates a noise (conductive noise) component having a relatively high frequency when the inductive load is operated, the xcfx80-type filter circuit and T-type filter circuit cannot filter and eliminate the generated noise component and the noise component generated from the inductive load affects other structural components in some cases.
The present invention has been accomplished in view of the technical background as described hereinabove, and it is the object of the present invention to provide a power source filter circuit that is capable of filtering and eliminating both various noise components included in a direct current supplied from a direct current power source and a noise component generated from a load effectively.
To accomplish the abovementioned object, a power source filter circuit in accordance with the present invention has a means provided with a first inductor and a second inductor connected in series between an input terminal and an output terminal, a first capacitor being connected between the input terminal and a reference potential point, a second capacitor being connected between the contact point that connects the first inductor with the second inductor and the reference potential point, a third capacitor being connected between the output terminal and the reference point, and a second being connected to the second inductor in parallel.
Furthermore, in the power source circuit in accordance with the present invention, a direct current power source is connected to the input terminal, an induction load is connected to the output terminal, and a direct current generated from the direct current power source is supplied to the induction load through the first inductor, second inductor, and resistance.
According to the abovementioned means, relatively low frequency various noise components included in a direct current supplied from a power source are filtered and eliminated by a xcfx80-type filter circuit comprising a first inductor, a first capacitor, and a second capacitor, and relatively high frequency various noise components included in the direct current are filtered and eliminated by a parallel circuit comprising a second inductor and resistance that exhibits low impedance to the high frequency noise and by a xcfx80-type filter circuit comprising a second capacitor and third capacitor. As the result, the direct current supplied to an output terminal does not include the various noise components. Furthermore, the relatively high frequency noise component generated from a load is filtered and eliminated similarly by a parallel circuit comprising a second inductor and resistance that exhibits low impedance to the high frequency noise and by a xcfx80-type filter circuit comprising a second capacitor and third capacitor. As the result, the noise level of the noise component generated from the load is reduced, and the noise component does not affect other structural components adversely.
In the power source filter circuit in accordance with the present invention, the resistance comprising two resistances connected in parallel is used.
By applying the abovementioned structure, the heat generation of the resistance is reduced even though a large current flows through the resistance, and the skin effect of the resistance to the relatively high frequency noise component is eliminated.
Furthermore, in the power source filter circuit in accordance with the present invention, an integrated resistance value is as small as 10xcexa9 or smaller.
The power source filter circuit having the structure as described hereinabove causes the direct current voltage drop due to connection of a resistance scarcely, and exhibits low impedance to the relatively high frequency noise component.